Those skilled in the art know the long history of development of microphones and pickups for musical instruments. Yet none have fully addressed the unique requirements for acoustic stringed musical instruments, such as guitars, dulcimers, harps, zithers, harpsichords, pianos, and other stringed musical instruments.
One means to pick up musical instrument sounds is by the use of microphones, such as an air microphone placed near or inside a musical instrument or a contact microphone affixed to a musical instrument. Difficulties in using microphones to amplify acoustic string instruments, particularly in live stage settings, have long been recognized by those skilled in the art. Considerable care must be taken in microphone selection and placement relative to the musical instrument in order to faithfully capture the instrument's tone. In addition, particularly for live performances, great care must be taken in amplifier adjustments and in the placement of loud speaker(s) in order to avoid acoustic feedback, caused when some resonant sound(s) generated by the loud speaker(s) feeds back to the microphone at a resonant frequency or frequencies, greatly reinforcing itself each time the sound is picked up by the microphone and amplified again on its way back to the loud speaker, causing the all-too-familiar feedback squeal, which can be damaging to equipment and painful to hear.
It has long been recognized by those skilled in the art that the current practice of electromagnetic pickup for vibrating tuned forks (e.g., U.S. Pat. No. 1,906,985, May 2, 1933, W. A. Marrison, Vibratory Frequency Standard) and for stringed musical instruments, for example, as on an electric guitar (e.g., U.S. Pat. Nos. 2,175,325, Oct. 10, 1939, H. S. Sunshine, Magnetic Pick-Up Device for Stringed Musical Instruments; 2,455,575, Dec. 7, 1948, C. L. Fender, et. al., Pickup Unit For Instruments; 2,573,254, Oct. 30, 1951, C. L. Fender, Combination Bridge and Pickup Assembly for String Instruments; 2,896,491, Jul. 28, 1959, S. E. Lover, Magnetic Pickup for Stringed Musical Instrument; 3,090,274, May 21, 1963, C. L. Fender, Electric Piano; 4,220,069, Sep. 2, 1980, L. C. Fender, Electromagnetic Pickup For Stringed Musical Instruments), does not capture the full tonality of the instrument. Indeed it is common practice for an electric guitar to have multiple sets of pickups, located at various distances between the bridge and fret board, in order to capture varying tonal characteristics. An electromagnetic pickup, generally consisting of a magnet and coil assembly, senses vibrations of ferro-metallic strings in the immediate vicinity of its magnetic coil, which typically encompasses only a very small portion of the total string length. While different electromagnetic pickups along the length of a vibrating string all sense the string's fundamental vibration (or note), each pickup emphasizes the string's harmonic vibrations present at that point on the string, causing each pickup along a string to produce different, often distinct, musical coloring or tone. Use of electromagnetic pickups necessitates the use of strings made with ferrous or ferrous-like alloys (such as nickel or phosphor bronze), to enable string vibrations to induce an electric current in the pickup coil, making electromagnetic pickups unsuitable for acoustic instruments using non-ferrous strings such as silver or nylon.
An alternative to the electromagnetic pickup is the piezoelectric element, often built-in to the bridge assembly and in contact with the musical instrument's strings (e.g., U.S. Pat. No. 2,222,057, Nov. 19, 1940, Hugo Benioff, Stringed Musical Instrument; U.S. Pat. No. 6,078,006, Jun. 20, 2000, H. Raisanen, et. al., Stringed Musical Instrument Transducer and Procedure for Its Fabrication; U.S. Pat. No. 6,515,214, Feb. 4, 2003, Yojiro Takabayashi, Pickup Unit Incorporated in Stringed Instrument for Converting Vibrations of String to Electric Signal in Good Fidelity). Although a single piezoelectric element may be used on, in, or near an instrument, such as a contact, tail, or bridge pickup, common practice is to use one (or more) piezoelectric element(s) under each string as it crosses the bridge assembly. In general this arrangement is preferred in order to better capture the instrument's tone. Due to the intricate relationships of string, piezoelectric element, and instrument bridge, piezoelectric elements are typically built into a musical instrument at time of manufacture. Electrical output of the piezoelectric elements is combined for use by an amplifier.
Another alternative to the electromagnetic pickup is the electrostatic pickup, which has a long history for reed organs (e.g., GB 434,421, Aug. 27, 1935, A. H. Midgley, Apparatus for Producing Sounds of a Musical Character; U.S. Pat. No. 2,015,014, Sep. 17, 1935, F. A. Hoschke, Musical Instrument; U.S. Pat. No. 2,318,936, May 11, 1943, R. C. Fisher, Multifrequency Oscillator; U.S. Pat. No. 2,462,531, Feb. 22, 1949, B. Minshall, Musical Vibration Translating Unit; U.S. Pat. No. 2,542,611, Feb. 20, 1951, V. I. Zuck, Pickup for Electric Organs; U.S. Pat. No. 2,911,870, Nov. 10, 1959, H. G. Bauer, Organ Reed Support Assembly), organs with rotating disks (e.g., U.S. Pat. No. 1,785,915, Dec. 23, 1930, F. M. Robb, Sound Reproducing Instrument; BE 451,466, 31 Aug. 31, 1943, N. V. Philips, Gloeilampenfabrieken; U.S. Pat. No. 1,996,669, Apr. 2, 1935, L. E. A. Bourn, Electrical Musical Instrument; U.S. Pat. No. 2,001,708, May 21, 1935, W. F. Curtis, Production of Music; GB 454,783, Oct. 6, 1936, A. H. Midgley, Apparatus for Producing Sounds of a Musical Character; U.S. Pat. No. 2,176,525, Oct. 17, 1939, F. A. Firestone, Electrical Musical Instrument; U.S. Pat. No. 2,214,764, Sep. 17, 1940, L. Hammond, Electrical Musical Instrument; U.S. Pat. No. 2,770,995, Nov. 20, 1956, G. R. Stibitz, Wave Form Generator; U.S. Pat. No. 2,921,494, Jan. 19, 1960, D. J. Leslie, Electrostatic Musical Tone Generator System; U.S. Pat. No. 2,952,179, Sep. 13, 1960, C. W. Andersen, Electronic Piano; ES 291,473, Nov. 16, 1963, J. A. Dereux, Dispositif de Silence pour Orgue Electro-Statique; U.S. Pat. No. 3,621,106, Nov. 16, 1971, J. M. Irastorzo, Electronic Tone Generator; FR 2,187,170, Jan. 11, 1974, Rameau (SA), Piano Electronique; U.S. Pat. No. 3,259,683, Jul. 5, 1966, D. J. Tomcik, Electric Organ), pianos with vibrating rods, bars, or strings, (e.g., U.S. Pat. No. 1,915,859, Jun. 27, 1933, B. F. Miessner, et. al., Method and Apparatus for the Production of Music; U.S. Pat. No. 1,952,630, Mar. 27, 1934, N. A. Palmgren, Musical Instrument; U.S. Pat. No. 2,986,963, Jun. 6, 1961, E. M. Jones, Electropiano, U.S. Pat. No. 3,139,476, Jun. 30, 1964, O. J. Alvarez, Elecrical Musical String Instrument; U.S. Pat. No. 3,334,174, Aug. 1, 1967, T. Shiga, et. al., Electronic Musical Instrument), carillons (e.g., U.S. Pat. No. 2,261,346, Nov. 4, 1941, G. W. Demuth, Electric Carillon; U.S. Pat. No. 2,284,911, Jun. 2, 1941, L. A. Maas, Musical Instrument; U.S. Pat. No. 2,582,441, Jan. 15, 1952, J. T. Kunz, Electric Bell Tone Generator Mechanism), accordions (e.g., U.S. Pat. No. 2,368,842, Feb. 6, 1945, Y. K. Kealoha, Musical Instrument), music boxes (e.g., U.S. Pat. No. 2,018,924, Oct. 29, 1935, R. H. Ranger, Apparatus for Producing Musical Tones); harmonica (e.g., U.S. Pat. No. 3,322,875, May 30, 1967, J. B. Roll, et. al., Harmonica Electronic Amplification), electrostatic contact or internal microphones (e.g., U.S. Pat. No. 2,228,881, Jan. 14, 1941, M. F. Le Clair, Music Producing Apparatus; U.S. Pat. No. 4,230,013, Mar. 21, 1979, F. L. Wellings, Electro-Acoustic Transducer; U.S. Pat. No. 4,495,641, Jul. 11, 1983, R. Vernino, Microphone Pickup for Musical Instruments; U.S. Pat. No. 4,995,293, Feb. 26, 1991, P. N. Anderson, Acoustic Instrument with Internally Positioned Microphone Means for Receiving Acoustical Vibrations), and phonograph pickups (e.g., GB 524,619, Aug. 12, 1940, Steatit-Magnesia A G, Improvements in and Relating to Electrostatic Recorders and Pick-Ups; U.S. Pat. No. 2,623,996, Dec. 30, 1952, J. W. Gray, Capacity Motion Responsive Device). However, the development of electrostatic pickups largely neglected the unique requirements for acoustic stringed musical instruments and has received little attention in recent years.
In 1949, Julius W. Gebhardt (near Poukeespie, N.Y.; now deceased; personal communications) experimented with electrostatic pickups for acoustic stringed musical instrument. Based on his reading at the time of some of the previously cited early patents for capacitive pickups in pianos and reed organs, he devised a novel approach to overcome many of the aforementioned limitations. Instead of using reeds or rotating disks, Gebhardt experimented with using one or more musical instrument strings for one side of a capacitive electrostatic pickup and a charged metal plate as the other side. He charged the metal plate with 240 volts direct current (DC), using electricity from the high-voltage direct-current power supply commonly available in vacuum-tube amplifiers, with a DC blocking capacitor to recover the signal created by string vibrations. During the following years, he installed his system on several concert zithers for his own use without applying for a patent on his pickup system.
The concert zithers on which Mr. Gebhardt installed his pickups had 5 fret board strings and 30 or more accompaniment strings, with one pickup plate under each group of strings; both pickup plates were attached to the instrument with standoffs and screws. To prevent unwanted contact with the plates, a pick guard was placed above the fret-board pickup plate and strings; the pickup plate for the accompaniment strings was placed under the strings away from the area being plucked. The pick guard above the fret-board strings limited the area in which the pick could be used, somewhat altering the position of the player's hand.
In spite of the pick guard and paint covering the plates, occasional accidental contact of a player's fingers or pick with a pickup plate would impart an unpleasant electrical shock to the player (akin to touching a doorknob after walking on a carpet during low-humidity winter weather). In addition, sudden uncontrolled electrostatic discharge created sudden intense crackling noise on the output signal of the DC blocking capacitor, sending potentially damaging noise pulses to connected equipment and speakers, which listeners would experience as loud, sharp, crackling noise.
There are two other issues with the prior art of electrostatic capacitive pickups for stringed instruments, including Gebhardt's embodiment. First, mounting the pickup plate(s) required attaching each plate with at least three screws penetrating into the body or structure of the instrument. The invasive nature of the screws embedded in the body of the musical instrument, along with the rigid attachment of metal plate(s), offered the distinct possibility of altering the musical tonal properties of the acoustic instrument to which they were attached. In at least one case, some players felt that the long pickup plate on a zither under the accompaniment strings physically muted the sound of an instrument, weakening its tone. The permanent nature of the pickup plate mounting made their removal difficult, discouraging unimpaired use of an instrument either with or without its pickup(s) at player discretion.
Another issue is the need for a high-voltage electric charge for the pickup plate, typically over 240 volts DC. Gebhardt used a wire to a vacuum tube amplifier's plate power supply. While simple and effective, it required a tube amplifier and modification to the amplifier by a qualified service person. For portable use with an unaltered amplifier, a 240-volt battery, made specifically for portable tube radios, could be used. However, as transistor radios became popular, portable tube radios and their high-voltage batteries became harder to obtain, eventually becoming obsolete.
The present invention as described hereinbelow is directed at improvements to the prior art, exemplified by Gebhardt as related above, of electrostatic pickup systems for stringed musical instruments; specifically, the present invention is safe to handle, preventing shock hazard to player and attached electronic equipment, allows pickup assemblies to be easily attached and removed without invasive alteration of the instrument, blocks stray electrical hum and noise, operates from a small portable battery-powered, or plug-in, power supply, may be used with existing music sound systems, captures the tone of the musical instrument, and is simple to manufacture with common materials and practices.